In my undergraduate studies one of the courses that most influenced my later thinking was an introduction to moral reasoning. I came out of it a committed utilitarian which only made life more difficult as given my favoured position in society – especially given global economic inequality. In principle I still believe I am morally obligated to give all but the bare minimum of what I own to help those in greater need elsewhere, but few of us can manage that.

He points out that even if only the top 10% of the US population (those on at least $92,000) gave a sizeable (10%+) proportion of their income annually (sums he implicitly contends they would not miss) that in itself would provide 8x the shortfall in the amount needed for the world to reach the UN’s millennium development goals. It certainly gives me something to shoot for once I am no longer a student.
See also this blog post of mine about Singer and Zell Kravinsky.